Speaking at the University of Huddersfield on Wednesday where he was awarded an honorary doctorate, Mr Mallinson said he and his three colleagues, Rick Stanton, John Volanthen and Chris Jewell, were in the process of making the documentary, which may be filmed in the UK.

Over half the tunnel was underwater – “you couldn’t see a hand in front of your face” – and the boys had to be sedated for their safety and that of their rescuers.

Mr Mallinson, who brought four of the boys to safety, including the last to be brought out, said: “There was a chance they would have panicked, and if they had they could have killed us as well by ripping our masks off or pulling the regulators out of our mouths.

“The only option was to sedate them so they were sleeping when they came out.

“I didn’t have many hairy moments. It is just keeping your head together and getting through the pinch points without getting into a fluster or a panic.”

He said visibility was so bad "you didn't realise a lot of the time you were in a pinch point until you were stuck in a corner.

"You'd have to move sideways, left or right, to get through.

"It was over two or three hours to get them out and maybe 10 or 12 pinch points."

He said he was "surprised" when the University decided to give him the award, but was happy to accept.

The latest award comes on top of the Queen’s Gallantry Medal which he has already received along with an Outstanding Bravery Award at the Pride of Britain Awards 2018.

Mr Mallinson, who went to High End Moor High School and Salendine Nook Sixth Form College, began diving in the Yorkshire Dales in 1985 and started cave diving four years later.